Button fastener



FIG. 1 is a perspective view of a button fastener showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a left side elevational view thereof, the opposite side being a mirror image;

FIG. 4 is a top plan view thereof; and,

FIG. 5 is a bottom plan view thereof. 

The ornamental design for a button fastener, as shown and described. 